Effects of treatment with immunomodulatory drugs on thymus and spleen lymphocyte subpopulations and serum corticosterone levels.

Immunofluorescence was used to characterize the lymphocyte subpopulations of mice treated with six immunomodulatory drugs: hydrocortisone acetate (HCA), corticosterone acetate (corticosterone), cyclophosphamide, cytosine arabinoside (Ara-C), 15(S)-methyl prostaglandin E1 (15(S)-methyl PGE1), and 2-amino-5-bromo-6-phenyl-4-(3H)-pyrimidinone (ABPP). The number of thymus and spleen cells bearing Thy-1, Ig, Lyt-1 and Lyt-2 antigens and the density of the antigens on each cell (IF profiles) were determined. Microscopic examination of cells stained with rhodamine-labeled anti-Lyt-2 and fluorescein-labeled anti-Lyt-1 was used to measure the proportion of Lyt-1+2-, Lyt-1+2+, and Lyt-1-2+ cells in the spleen and thymus of drug-treated animals. The changes in lymphocyte subpopulations were compared with the varied effects of these drugs on antibody formation and graft vs host (GVH) reaction. Three immunosuppressive drugs, HCA, cyclophosphamide, and Ara-C, depleted the thymus of cells expressing a large quantity of Thy-1. The drug-resistant cells were larger and had more Lyt-1 than cells from control animals. HCA treatment depleted the thymus of Lyt-1+2+ cells; the cortisone resistant cells were primarily Lyt-1+2-. Cyclophosphamide and the antiviral immunostimulant, ABPP, caused similar, but less marked, alterations. The proportion of Lyt-1-2+ cells in the thymus was reduced by treatment with all the drugs, but the density of Lyt-2 on the drug-resistant cells was not altered. Treatment with Ara-C or 15(S)-methyl PGE1 produced a very modest evaluation in Lyt-1+2- cells. 15(S)-Methyl PGE1, which suppresses some immuno-inflammatory reactions, had no discernible effect on thymocyte size or the IF profile of Thy-1, Lyt-1, or Lyt-2. In the spleen, the amount of Thy-1 and of immunoglobulin on cells bearing these markers was changed very little by drug treatment. The proportion of splenic B cells was diminished by treatment with cyclophosphamide and, to a lesser extent, by HCA, while the proportion of spleen cells bearing detectable Thy-1 and Lyt-1 increased correspondingly. The proportion of cells bearing Lyt-2 was altered by only two drugs; cyclophosphamide increased both Lyt-1+2+ and Lyt-1-2+ spleen cells and ABPP (an interferon inducer which stimulates antibody formation) decreased both Lyt-2+ subpopulations. Treatment with two drugs caused the serum corticosterone concentration to rise: ABPP increased serum corticosterone substantially while the prostaglandin induced a smaller and more transitory increase. An indirect mechanism, via corticosteroid release, might explain the thymic depletion observed in mice treated with 15(S)-methyl PGE1 and ABPP, but neither the suppression of the GVH reaction by these drugs nor polyclonal activation of B cells by ABPP can be attributed to endogenous corticosteroids. Our data show that enumeration of splenic lymphocyte subpopulations by immunofluorescence techniques may aid in elucidating the mode of action of immunomodulatory drugs.